Filters for X-Ray film (Fuji HRT-Green)

[Toffle]

Has anyone here done the leg work to test the use of standard black and white filters with orthochromatic films?

I've been shooting the Fuji HRT Green film for two or three years, and I'm quite familiar with it under most conditions, but I've never really used my standard black and white filters to manipulate contrast. Recently I have begun experimenting with a couple of filters, (mostly yellow and orange) but my results have been generally disappointing. I'm having difficulty making the switch from what I expect from panchromatic film and filter combinations to the green sensitive HRT. I suspect I'm still moving in the wrong direction in terms of contrast.

Basically, I'm looking for filters to darken clouds and skies the way a red #2 would with panchromatic films.

As a short side note, very early in my experience with HRT, I learned (the hard way) that this film does not pass the safe light test. I've even managed to make negatives using a red filter under very long exposures, but they're nothing I'd care to try to print.​

I'd be happy to hear of your experiences with X-Ray films and filters.

Cheers,
Tom

 

[Gerald C Koch]

Since this film is not intended for pictorial photography you would have to look at the spectral sensitivity curve for this film. This will tell you which filters would be effective and those that would not. The problem with x-ray films in general is that their sensitivity has been designed to match the imaging phosphors used in an x-ray machine.

 

[DWThomas]

Hi Tom,
I've been shooting some 8x10 pinhole stuff with HR-T but hadn't really thought about trying filters -- and the camera doesn't have a way to stick one on (other than literally sticking with some sort of tacky gunk (have to blame myself, the designer and builder!) \

Anyway my thought is that darkening a sky with a filter is normally attenuating blue light relative to other colors in the scene. Since HR-T apparently doesn't see much blue to begin with, that approach may not work. Although (dangerously thinking whilst typing here ...) if the film has reduced blue sensitivity a clear blue sky should come out at least somewhat darker anyway. My suspicion is that contrast filtering is likely to be much less effective on an orthochromatic film because (very) loosely speaking it only sees one color so we can't really alter the intensity ratios of different color light rays within a scene. [yeh, very loosely ... ]

Hmmph -- howz-about a polarizer?!

In my WPPD efforts this year I did some more exploring with a red LED safelight bulb (SuperBright E27-R8-G) with HR-T. I had it in a classic Kodak bullet safelight fixture and ended up using a Rubylith red filter AND a two stop ND filter (laser printed on overhead projector film!), all stacked on an acrylic disk, to get working time out past 10 minutes (approx 42 inches above bench). It seems HR-T does have some red sensitivity (or maybe my Rubylith is a bit orange -- it is at least 30 years old anyway). That bulb's unfiltered light intensity is dazzling compared with a Wratten #2 dark red and 15w incandescent, so even with my homebrew filtering it's brighter.

 

[Jim Noel]

no new research required. Simply lookup information on Orthochromatic films and their uses in any decent text or magazine article prior to about 1940. I use the samechart i used with Tri-X Ortho flm

 

[juan]

I think Jim is right. I've used K-1 and 2 filters successfully with green X-ray film. Orange filters have not worked for me - little or no image - but that might mean a need to give a lot more exposure.
Juan

 

[DWThomas]

I think Jim is right. I've used K-1 and 2 filters successfully with green X-ray film. Orange filters have not worked for me - little or no image - but that might mean a need to give a lot more exposure.
Juan

You raise a good point -- published filter factors are likely dubious when moving away from panchromatic emulsions.

 

[Toffle]

Thanks for the suggestions, folks.
It appears I may chasing chimeras to a certain extent. Despite the film's known characteristics, I've been trying to nudge it a little to give myself a little more control over what I bring into the darkroom to print, but I may be using the wrong set of tools. (beginning with film choice... anyone else notice that it appears I'm trying to make the film behave precisely the way it is designed not to work?) There is some reasoning behind this, most simply put that while I really like using this film, it's not all that versatile, and I'd like to tweak it a little to see how much I can achieve in that respect.

Juan, I've taken a few shots with a K2, but they are actually more difficult to print than similar, unfiltered shots. It may be just a matter of nailing down the exposure, but to date, I'm still ending up with muddy-looking skies.

Cheers,
Tom

 

[Toffle]

You raise a good point -- published filter factors are likely dubious when moving away from panchromatic emulsions.

Dave, you posted this while I was composing my other response. I totally agree, and this more or less hinges on the question I phrased so badly in the OP. What I'm trying to learn is, given the heavy weighting of HR-T towards the blues and greens, what are the effects of different filters on what light reaches the film? What can I hope to accomplish, and how much of a filter factor need I apply to get good results?

 

[DWThomas]

Dave, you posted this while I was composing my other response. I totally agree, and this more or less hinges on the question I phrased so badly in the OP. What I'm trying to learn is, given the heavy weighting of HR-T towards the blues and greens, what are the effects of different filters on what light reaches the film? What can I hope to accomplish, and how much of a filter factor need I apply to get good results?

OK (after two morning coffees) I'm thinking one could create a series of step charts in gray and a few handy colors (created and printed with technology not normally discussed here ) and shoot some tests to see what values change. I suppose one might even very loosely obtain a sense of spectral sensitivity that way. Could also include a color printed "scene" with white fluffy clouds against some various blues.

[If all else fails, maybe the test target could make it into an art show ]

With IR rollfilm I have done some tests with various filters just using a few bracketed shots with each filter, but shooting a wide range of tests with 8x10 sheets is a bit tedious! I might go 1/4-sheets in a 4x5 should I ever decide to try it.

 

[Thomas Bertilsson]

Well, X-ray film is blue and green sensitive, which explains why an orange filter will not work. Orange is the complimentary color of blue, and will filter out virtually ALL blue light that reaches the camera, and most of the green too, since orange has a fair amount of red in it (the complimentary color of green).
The yellow will also filter out most of the blue, but should let through some components of green light.

Now, photographic paper has similar sensitivity to X-Ray film, so it would make more sense to experiment with darkroom printing filters, unless the film is only either green or blue sensitive, in which case those filters won't work either.

 

[Jim Noel]

I think Jim is right. I've used K-1 and 2 filters successfully with green X-ray film. Orange filters have not worked for me - little or no image - but that might mean a need to give a lot more exposure.
Juan

The lack of an image through an orange filter simply means the film is not sensitive to the color. Orange is too red to be recorded.

 

[Jim Noel]

You raise a good point -- published filter factors are likely dubious when moving away from panchromatic emulsions.

Look at the old sources which list filter factors for ortho films.

 

[Toffle]

The yellow will also filter out most of the blue, but should let through some components of green light.

Now, photographic paper has similar sensitivity to X-Ray film, so it would make more sense to experiment with darkroom printing filters, unless the film is only either green or blue sensitive, in which case those filters won't work either.

Ok... That's what I was hoping to accomplish with the K2, but the results were decidedly muddy. (skies are particularly tricky with X-Ray film anyway, but I was hoping to improve on that)

As to your second point, Thomas, I'm a little confused. I considered this early on in the process, but a particular thought held me up. I was under the impression that there were two different emulsion layers on the paper, and the filters were to determine which proportion of the low or high contrast layers are exposed under the enlarger. (Hey, I read it on the internet, it must be true! ) At any rate, the negatives themselves are monochrome. I'm not sure how that would translate to the film. It's worth a try, I guess.

Cheers,
Tom

 

[Toffle]

Look at the old sources which list filter factors for ortho films.

Hi Jim! You mentioned something to this effect last night, and I spent a couple of frustrating hours trying to find precisely this information. A fresh search this morning was a little more fruitful, but I'll have to spend some time sifting through what I've found to see what it's telling me.
Thanks.

 

[Thomas Bertilsson]

Ok... That's what I was hoping to accomplish with the K2, but the results were decidedly muddy. (skies are particularly tricky with X-Ray film anyway, but I was hoping to improve on that)

As to your second point, Thomas, I'm a little confused. I considered this early on in the process, but a particular thought held me up. I was under the impression that there were two different emulsion layers on the paper, and the filters were to determine which proportion of the low or high contrast layers are exposed under the enlarger. (Hey, I read it on the internet, it must be true! ) At any rate, the negatives themselves are monochrome. I'm not sure how that would translate to the film. It's worth a try, I guess.

Cheers,
Tom

Yes, VC papers have two emulsion layers. I was hoping X-Ray film did too. The VC filters adjust the ratio of blue and green light that's let through to the paper, thus adjusting contrast.

If the X-Ray film is only blue OR green sensitive, then the only thing that will happen is that the filters will let through X amount of blue or green light, so the VC paper filters would sort of serve as ND filters.

 

[Toffle]

Ideally you'd have some info on the sensitivity of this film. I can't find any Fuji numbers on HRT specifically, but since it is described by Fuji as orthochromatic, in addition to standard blue sensitivity it likely has an additional peak in the middle of the green spectrum to increase overall speed. Note this is not truly orthochromatic since sensitivity is not continuous from blue through green, but instead has specially designed peaks.

Assuming the above is true, if you want dark skies (blue), a reasonable starting point would be to use green filters. You'd have to experiment with the type, from yellow-green to tricolor green (which will pass only green) to blue-green (which will pass some blue).

Of course you can expect significant speed losses (which will also be highly variable under different lighting), and will have to experiment to find something that gives you the tone reproduction you're looking for.

I couldn't find detailed curves specifically for the HR-T either, but the data for the HR-S confirms what you say about peaks for both blue and green.

Note, despite what you may have heard, the film is not truly blind to the red end of the spectrum; its response is just so low that it is effectively so. One of the first things I did when I started using HR-T a few years ago is to do a safe light test, and it didn't pass. (so despite the assurances, I only work under the dimmest lighting in the darkroom) This is what got me wondering about the overall response of the film to filters. I did try a shot using an R2 filter, and a two-minute exposure at f4.5 gave me an ugly, but theoretically usable negative. (compared to 1/25 sec without a filter) It seems that I've been struggling with the line between ugly and theoretically usable ever since.

It certainly is incentive to be extra careful of my process from metering, filtering, processing and printing. (But I'm not quite getting the results I'm hoping for.)

 

[Kobin]

X-ray film is part of an analog imaging system in which a number of x-ray photons are absorbed by a phosphor screen in the film holder, which then emits many more photons of visible light in a frequency range dictated by the composition of the phosphor. Calcium tungstate fluoresces with blue light, and rare earth compositions flash green. Of course, blue sensitive film requires blue-flashing screens to make an image, and green sensitive film is only sensitive to a range of green light extending into amber (OC safelights will fog green film). So yes, the film is either blue sensitive or green sensitive. There is no doubt some overlap in the spectral responses of the films, but not enough to make each equally responsive to light coming through a given filter.

So, blue sensitive film may respond like photographic othrochromatic film when used pictorially, but green film has will have a somewhat different response when used the same way. To confuse matters more, in radiology parlance green sensitive film was called "ortho" film, while blue sensitive film was called "regular".

K.

 

[Andrew O'Neill]

I did some testing with green latitude x-ray a few years back with yellow and green filters. I used a Wratten #8, #15, #11 (light green). The filtered results were always better than unfiltered.

 

[Toffle]

Ok...

During a break in today's otherwise incessant cloud cover, I dashed off two test shots. (Subject matter: land, trees, sky, clouds and water... fairly representative of the view out my back door)

Sans filter, exposure was 1/25 @f22 (Ektar 203 f7.7 one of my favourite lenses). With the above noted K2 I dialed back a couple of EV, which gave an exposure of 1/5 @f22. As it turns out the two negatives are nearly identical, though the filtered shot is marginally less dense. In neither negative can I see clear definition between the clouds and the sky. (There's plenty of contrast between the land features, but very little between the sky, clouds and water) A quick read of the negatives suggests substantial burning in to get any detail in the sky. (For the purpose of this test, I will do my best to resist any temptation to manipulate the prints, though I suspect a straight print of either of these negatives will yield unsatisfactory results.)

I will try to do a straight print of each negative this evening. (but with two toddler grandchildren to babysit tomorrow, I may have to forego this part of the test for another day)

Thanks for the encouragement. I appreciate the knowledge and expertise of my fellow APUGgers.

Cheers,
Tom

EDIT/UPDATE:
There were some brilliant skies during the rapidly fading sunset this evening. I managed two more exposures, 5s @f16 without filter. and 25s @f16 with filter. There was a lot more variance in the sky, so I'm hopeful that the resulting negatives will have more detail by which to judge the effects of the K2 filter.

 

[apkujeong]

I've been using Agfa Ortho CP-G plus, no problems getting clouds to show up with that and a light yellow filter. I got some cloud definition without a filter, I think. I've also been using Agfa Mamoray in 18x24, also cut down to 9x12.

About filters, the third page of this pdf has a table of common filters and their uses with ortho / pan film, I don't know the origin but here it is:

http://www.ohio.edu/people/schneidw/vico222/222Handouts/295filtr.pdf

 

[Toffle]

I've been using Agfa Ortho CP-G plus, no problems getting clouds to show up with that and a light yellow filter. I got some cloud definition without a filter, I think. I've also been using Agfa Mamoray in 18x24, also cut down to 9x12.

About filters, the third page of this pdf has a table of common filters and their uses with ortho / pan film, I don't know the origin but here it is:

http://www.ohio.edu/people/schneidw/vico222/222Handouts/295filtr.pdf

I found that ortho film pdf last night whilst looking down the rabbit hole. It looks fairly concise and straight forward.

 

[Toffle]

Here are the results from yesterday's tests, with and without filter. Two daylight shots, which should show fluffy clouds and an expanse of clear sky, and two twilight shots in which there was brilliant banding of the clouds in the sunset. I'm not seeing much of that in either series, though the twillight photos are much cleaner. The problem I am getting is that any shots with bright skies (I am guessing high UV?) come out very mottled and muddy. For most of my printing over the past few years, I have been printing using Caffenol, so I had assumed this was a characteristic of the printing process, but recently I have been doing more traditional printing in a much more carefully monitored process, so this is definitely in the negatives. What is it about X-Ray film that causes this, and is there any way to mitigate it? Indoor/studio work, and anything away from expanses of open sky seem to be immune to this phenomenon.

Anyway, here are the shots: (Straight prints, with no print controls... just about killed me to refrain from burning the corners in)
First the daylight shots. No filter first, and then with the Yellow filter. I was hoping that the K2 would give me more definition in the clouds, and something pleasant in the sky. Note the lovely stucco texture of the sky.


Then the twilight shots:
These are somewhat better, and I can only guess it is because the skies were less blue, but that is only a guess. I didn't nail the exposures quite as well, but I wasn't exactly testing that. I was hoping for better contrast in the bands of clouds.


Suggestions?
[EDIT] Something weird going on with the attachments. I hope you can figure it out.

[EDIT 2] I'm currently running a test with/without a UV filter... Don't know why it never occurred to me before. Fingers crossed.

[EDIT 3] The above test was pretty much inconclusive, though the negatives are yet to be printed, but to be fair, the shots were taken pretty well into the twilight hour, so I might not expect much UV in any case.

Cheers,
Tom